1. Field
This disclosure relates generally to mapping and, more specifically, to techniques for resource block mapping in a wireless communication system.
2. Related Art
In general, orthogonal frequency division multiplexing (OFDM) systems support high data rate wireless transmission using orthogonal channels, which offer immunity against fading and inter-symbol interference (ISI) without requiring implementation of elaborate equalization techniques. Typically, OFDM systems split data into N streams, which are independently modulated on parallel spaced subcarrier frequencies or tones. The frequency separation between subcarriers is 1/T, where T is the OFDM symbol time duration. Each symbol may include a guard interval (or cyclic prefix) to maintain the orthogonality of the symbols. In general, OFDM systems have utilized an inverse discrete Fourier transform (IDFT) to generate a sampled (or discrete) composite time-domain signal.
Various wireless networks, such as third-generation partnership project-long term evolution (3GPP-LTE) compliant architectures, may be designed to employ uplink reference signals (RSs) for uplink carrier-to-interference and noise (CINR) estimation, which is used by a scheduler, e.g., a network scheduler, to schedule uplink transmission for user equipment (subscriber stations (SSs)). Respective sequences of the RSs are used to uniquely identify an SS and, when transmitted from the SS to a serving base station (BS), may be used by the serving BS in channel characterization. In general, a scheduler associated with one or more serving BSs utilizes information derived from channel characterization to determine channel allocation for the SSs. The channel allocation, e.g., uplink and downlink assignments, have then been provided to the SSs over a downlink shared control channel (physical downlink control channel (PDCCH)), which typically includes one or more control channel symbols. The one or more control channel symbols are usually transmitted by the serving BS at a beginning of a downlink frame (or subframe). Typically, upon receiving the one or more control channels symbols, each of the SSs searches (using, for example, a blind search procedure) the one or more control channel symbols to locate an associated downlink and uplink control channel to determine respective uplink and downlink assignments.
A known control channel downlink scheduling approach has proposed employing a resource block (RB) map in an associated downlink control channel of each SS. According to this approach, a bit is provided in the RB map for each RB that is to be scheduled. An RB may have various lengths, e.g., seven symbols, and correspond to a group of subcarriers, e.g., twelve subcarriers. As one example, in a conventional wireless communication system having a 20 MHz bandwidth, an RB map may employ one-hundred bits to support discontinuous RB assignment. In this case, a given SS searches an associated 100-bit RB map in an associated downlink control channel to determine a location of the RBs assigned to the given SS for downlink communication. For example, a digital one, e.g., a ‘1’, in a bit of the RB map may be used to indicate to an SS that an associated RB is assigned to the SS and a digital zero, e.g., a ‘0’, in a bit of the RB map may be used to indicate to the SS that an associated RB is assigned to another SS (or is unassigned).
With reference to FIG. 1, an example diagram 100 of a relevant portion of a downlink shared control channel that employs a conventional resource block (RB) mapping scheme is illustrated for five SSs (i.e., the SSs denoted as SS1, SS2, SS3, SS4, and SS5). As is shown, each associated downlink control channel (CCH) of the SSs includes an individual RB map that maps all of the RBs in a related wireless communication system. In this case, five-hundred RB mapping bits (i.e., one-hundred RB mapping bits per each of the five SSs) are required to be transmitted (from the serving BS to the five SSs) on a downlink shared control channel. While the number of conventional RB mapping bits may be limited to reduce overhead, reducing the number of RB mapping bits also results in a loss of scheduling gain. That is, reducing the number of conventional RB mapping bits reduces a size of a frequency spectrum that may be utilized for communication which may reduce frequency selectivity (i.e., an ability of a serving BS to choose a best RB or group of RBs for a given SS).
What is needed are techniques for reducing overhead associated with resource block mapping in a downlink shared control channel (of a wireless communication system) that do not adversely affect frequency selectivity.